Effective target tolerance in an inverted Fitts task

An inverted Fitts task is defined as one in which the subject moves a probe of large width to a target that may be smaller in width than the probe. This is the inverse of the normal task in which a pointed stylus is moved between targets of variable width. Four experiments are reported; in the first with pointed targets, it was found that Fitts' law applied in its normal form with information processing rates typical of those found in the usual method. The second experiment, using finite widths for both probes and targets, showed that Fitts' law applied when an 'effectiveapos; target tolerance, which was the sum of the fixed target width and about 0-6 of the probe width, was used in calculation of the Index of Difficulty. Two further experiments illustrated the use of effective target tolerance when the finger and the foot were used as a probe.